The present invention relates to superabsorbent thermoplastic compositions and to meltblown or spunbonded webs prepared therefrom.
Disposable absorbent products such as diapers, sanitary napkins, tampons, incontinence products, and the like typically are comprised of a batt or absorbent portion which is wrapped with a liner. The batt typically is comprised primarily of cellulose fibers and the liner usually is a nonwoven web of a polyolefin such as polyethylene or polypropylene.
In the past, significant efforts have been made to find ways to make such disposable absorbent products more efficient or more appealing to the consumer. Much of such efforts have focused on increasing the absorbent capacity of the product on a unit mass basis while at the same time increasing the ability of the product to retain absorbed fluid. The ability of a product to remove and keep body fluids from the skin is perceived as a desirable attribute and is believed to be a factor in the reduction of such skin problems as diaper rash.
Such increased absorbent capacity and fluid retention typically have been accomplished by incorporating a superabsorbent material into the absorbent batt. The superabsorbent material usually is in particulate form. Unfortunately, particulate superabsorbents often migrate in or fall out of the absorbent product and/or exhibit gel-blocking, a phenomenon which prevents the migration of fluid into the central portion of the superabsorbent particle. Moreover, the use of particulate superabsorbents complicates the manufacturing process and the particulate nature of the superabsorbents limits the applications for the superabsorbents.
Superabsorbent materials, also referred to as hydrogels, frequently are based on acrylate and methacrylate polymers and copolymers. Other hydrogels are based on starch or a modified starch. Hydrogels prepared from hydrolyzed crosslinked polyacrylamides and crosslinked sulfonated polystyrenes or based on maleic anhydride (or similar compounds) have been described. Finally, still other hydrogels are based on polyoxyalkylene glycols and include polyurethane hydrogels.
The known polyoxyalkylene glycol-based superabsorbents generally tend to come within one of the following classes, at least in so for as they are reasonably related to the present invention:
(1) crosslinked poly(oxyalkylene) glycols; PA1 (2) crosslinked isocyanate-capped poly(oxyalkylene) glycols, i.e., polyurethanes or polyureas; PA1 (3) polyurethanes prepared from polyfunctional prepolymers or resins and diisocyanates; PA1 (4) polyurethanes prepared from isocyanate-capped polyesters or poly(oxyalkylene) glycols and difunctional extenders; PA1 (5) polyurethanes prepared from poly(oxyalkylene) glycols, isocyanate-capped low molecular weight prepolymers, and polyfunctional low molecular weight components. PA1 (a) from about 86 to about 98 percent by weight, based on the total weight of the composition, of a poly(oxyethylene) soft segment having a weight average molecular weight in the range of from about 5,000 to about 50,000; and PA1 (b) from about 2 to about 14 percent by weight, based on the total weight of the composition, of a hard segment which has a melting point above ambient temperature and below the temperature at which decomposition of either the composition or the soft segment takes place, is essentially insoluble in water, and phase separates from the soft segment, said hard segment being selected from the group consisting of polyurethanes, polyamides, polyesters, polyureas, and combinations thereof; PA1 (A) from about 86 to about 98 percent by weight, based on the total weight of the composition, of a poly(oxyethylene) soft segment having a weight average molecular weight in the range of from about 5,000 to about 50,000; and PA1 (B) from about 2 to about 14 percent by weight, based on the total weight of the composition, of a hard segment which has a melting point above ambient temperature and below the temperature at which decomposition of either the composition or the soft segment takes place, is essentially insoluble in water, and phase separates from the soft segment, said hard segment being selected from the group consisting of polyurethanes, polyamides, polyesters, polyureas, and combinations thereof; PA1 (A) from about 86 to about 98 percent by weight, based on the total weight of the composition, of a poly(oxyethylene) soft segment having a weight average molecular weight in the range of from about 5,000 to about 50,000; and PA1 (B) from about 2 to about 14 percent by weight, based on the total weight of the composition, of a hard segment which has a melting point above ambient temperature and below the temperature at which decomposition of either the composition or the soft segment takes place, is essentially insoluble in water, and phase separates from the soft segment, said hard segment being selected from the group consisting of polyurethanes, polyamides, polyesters, and polyureas, and combinations thereof; wherein the soft and hard segments are covalently bound together by means of urethane, amide, ester, or secondary urea linkages or combinations thereof. PA1 (A) from about 86 to about 98 percent by weight, based on the total weight of the composition, of a poly(oxyethylene) soft segment having a weight average molecular weight in the range of from about 5,000 to about 50,000; and PA1 (B) from about 2 to about 14 percent by weight, based on the total weight of the composition, of a hard segment which has a melting point above ambient temperature and below the temperature at which decomposition of either the composition or the soft segment takes place, is essentially insoluble in water, and phase separates from the soft segment, said hard segment being selected from the group consisting of polyurethanes, polyamides, polyesters, polyureas, and combinations thereof; PA1 (A) from about 86 to about 98 percent by weight, based on the total weight of the composition, of a poly(oxyethylene) soft segment having a weight average molecular weight in the range of from about 5,000 to about 50,000; and PA1 (B) from about 2 to about 14 percent by weight, based on the total weight of the composition, of a hard segment which has a melting point above ambient temperature and below the temperature at which decomposition of either the composition or the soft segment takes place, is essentially insoluble in water, and phase separates from the soft segment, said hard segment being selected from the group consisting of polyurethanes, polyamides, polyesters, polyureas, and combinations thereof; PA1 (A) reacting a first compound with a second compound at a temperature of from about 50 to about 200 degrees C. for a time sufficient to effect essentially complete reation; and PA1 (B) reacting with the product from step A a third compound at a temperature of from about 80 to about 200 degrees C. for a time sufficient to obtain a melt flow rate of less than about 1,000 g per 10 minutes under the test conditions described hereinafter;